Cyclonic fluid separator with vortex generator in inlet section

ABSTRACT

A cyclonic fluid separator of the type comprising a tubular throat portion in which a fluid mixture is accelerated to a subsonic or supersonic speed and thereby expanded and cooled down so that condensable components condense and/or solidify and then swirl into a diverging fluid outlet section that comprises an outer secondary outlet for condensables enriched fluid components and an inner primary outlet for condensables depleted fluid components comprises swirl imparting vanes that protrude from a central body that extends through at least part of an inlet section of the separator, wherein the central body has, at a location upstream of the throat portion, a larger outer width (2R o max ) than the smallest inner width (2R n min ) of the throat portion.

FIELD OF THE INVENTION

The invention relates to a cyclonic fluid separator with a vortexgenerator located in an inlet section of the generator.

BACKGROUND OF THE INVENTION

Such cyclonic separators are known from Japanese patent No. 2017921,Russian patent No. 1768242, UK patent application No. 2035151 and PCTpatent application WO 00/23757.

The known cyclonic fluid separators comprise a tubular throat portion inwhich the fluid stream is accelerated to a possibly supersonic speed andrapidly cooled down as a result of adiabatic expansion. The rapidcooling will cause condensation and/or solidification of condensables inthe fluid stream into small droplets or particles. If the fluid streamis a natural gas stream emerging from a natural gas production well thenthe condensables may comprise water, hydrocarbon condensates, waxes andgas hydrates. These separators furthermore comprise an assembly of swirlimparting vanes in an inlet portion upstream of the throat portion,which vane or vanes are tilted or form a helix relative to a centralaxis of the throat portion to create a swirling motion of the fluidstream within the separator. The centrifugal forces exerted by theswirling motion on the fluid mixture will induce the relatively highdensity condensed and/or solidified condensables to swirl to the outerperiphery of the interior of the throat portion and of a divergingoutlet section whereas relatively low density gaseous components areconcentrated near the central axis of the separator. The gaseouscomponents are subsequently discharged from the separator through aprimary central outlet conduit, whereas the condensates enriched fluidstream is discharged from the separator through a secondary outlet whichis located at the outer circumference of the diverging outlet section.

A disadvantage of the known vortex generators in the inlet section ofthe separator is that the amount of rotation imposed on the fluid streamis limited, unless the blades of the vortex generator are oriented at alarge angle relative to the central axis of the separator, in which caseblades create a high flow restriction in the fluid stream.

SUMMARY OF THE INVENTION

The cyclonic fluid separator according to the invention theretocomprises:

a tubular throat portion which is arranged between a converging fluidinlet section and a diverging fluid outlet section that comprises anouter secondary outlet for condensables enriched fluid components and aninner primary outlet for condensables depleted fluid components; and

a number of swirl imparting vanes for creating a swirling motion of thefluid within at least part of the separator, which vanes protrude from acentral body that extends through at least part of the inlet section ofthe separator, wherein the central body has, at a location upstream ofthe throat portion, a larger outer width than the smallest inner widthof the throat portion.

The arrangement of the swirl imparting vanes on a large diameter centralbody around which the fluid stream is induced to flow and subsequentlyguided into the relatively small diameter throat portion will enhancethe speed of rotation of the fluid stream as a result of the phenomenaof preservation of moment of momentum.

The shape of the blade plane can be either flat of curved. It ispreferred that the tubular throat portion and the outer surface of thecentral body are substantially co-axial to a central axis of theseparator and the swirl imparting vanes protrude from the outer surfaceof the central body at or near an area where the central body has alarger outer width than other parts of the central body.

It is also preferred that the central body has a substantially circular,onion-like, shape and comprises upstream of the swirl imparting vanes adome-shaped nose section of which the diameter gradually increases suchthat the degree of diameter increase gradually decreases in downstreamdirection, and the central body further comprises downstream of theswirl imparting vanes a tail section of which the diameter graduallydecreases in downstream direction along at least part of the length ofthe tail section.

Preferably the degree of diameter decrease of the tail section of thecentral body varies in downstream direction such that the tail sectionhas an intermediate section of which the degree of diameter decrease issmaller than the diameter decrease of adjacent parts of the tail sectionthat are located upstream and downstream of the intermediate section. Insuch case the shape of the central body may be described as pear-shaped.

Suitably, the separator comprises a housing in which the central body isarranged such that an annulus is present between the inner surface ofthe housing and the outer surface of the central body. The width of theannulus may be designed such that cross-axial area of the annulusgradually decreases downstream of the swirl imparting vanes such that inuse the fluid velocity in the annulus gradually increases and reaches asupersonic speed at a location downstream of the swirl imparting vanes.In such case the width of the annulus may vary such that at theprevailing pressure difference between the inlet section and the outletsection during normal operation of the separator the fluid flowingthrough the annulus reaches a supersonic velocity at or near theintermediate section of the tail section of the central body.

Suitably, the tail section may comprise an elongated substantiallycylindrical downstream end, which extends substantially co-axial to thecentral axis through the throat portion and at least part of thediverging fluid outlet section of the separator. Said elongateddownstream end may serve as a vortex finder which stabilises andcentralises the vortex throughout a major part of the interior of thecyclonic separator. Optionally, a number of flow straightening vanes aremounted on the substantially cylindrical downstream end of the tailsection of the central body at a location within the diverging outletsection of the separator, as to transfer tangential momentum in tostatic pressure increase.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in more detail, by way of example, withreference to the accompanying drawing.

FIG. 1, which depicts a longitudinal sectional view of a cyclonicseparator according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown a cyclonic inertia separatorwhich comprises a swirl inlet device comprising a pear-shaped centralbody 1 on which a series of swirl imparting vanes 2 are mounted andwhich is arranged co-axial to a central axis I of the separator andinside the separator housing such that an annular flow path 3 is createdbetween the central body 1 and separator housing. The separator furthercomprises a tubular throat portion 4 from which in use the swirlingfluid stream is discharged into a diverging fluid separation chamber 5which is equipped with a central primary outlet conduit 7 for gaseouscomponents and with an outer secondary outlet conduit 6 for condensablesenriched fluid components. The central body 1 has a substantiallycylindrical elongate tail section 8 on which an assembly of flowstraightening blades 9 is mounted. In accordance with the invention thecentral body 1 has a largest outer width or diameter 2 R_(o max) whichis larger than the smallest inner width or diameter 2 R_(n min) of thetubular throat portion 4.

The functions of the various components of the cyclonic fluid separatoraccording to the invention is as follows.

The swirl imparting vanes 2 which are oriented at an angle (α) relativeto the central axis I create a circulation (Γ) in the fluid stream. Itis preferred that a is between 20° and 30°. The fluid stream issubsequently induced to flow into the annular flow area 3. Thecross-sectional surface of this area is defined as:A_(annulus)=π.(R_(outer) ²−R_(inner) ²) The latter two being the outerradius and inner radius of the annulus at a selected location. The meanradius of the annulus at that location is defined as:R _(mean)=√[½(R _(outer) ² +R _(inner) ²)]

At the maximum value of the mean annulus radius R_(mean,max) the fluidstream is flowing between the assembly of swirl imparting vanes 2 at avelocity (U), which vanes deflect the flow direction of the fluid streamproportional to the deflection angle (α) and so obtaining a tangentialvelocity component which equalsU _(φ) =U. sin(α) and an axial velocity componentU _(x) =U. cos(α).

In the annular space 3 downstream of the swirl imparting vanes 2 theswirling fluid stream is expanded to high velocities, wherein the meanannulus radius is gradually decreasing from R_(mean,max) toR_(mean,min).

It is believed that during this annular expansion two processes occur:

-   (1) The heat or enthalpy in the flow (h) decreases with the amount    Δh=−½ U², thereby condensing those flow constituents which first    reaching phase equilibrium. This results in a swirling mist flow    containing small liquid or solid particles.-   (2) The tangential velocity component increases inversely with the    mean annulus radius U_(φ) substantially in accordance with the    equation U_(φ, final)=U_(φ, initial)·(R_(mean, max)/R_(mean, min)).    This results in a strong increase of the centrifugal acceleration of    the fluid particles (a_(c)), which will finally be in the order of:    a _(c)=(U _(φ, final) ² /R _(mean, min)).

In the tubular throat portion 4 the fluid stream may be induced tofurther expand to higher velocity or be kept at a substantially constantspeed. In the first case condensation is ongoing and particles will gainmass. In the latter case condensation is about to stop after a definedrelaxation time. In both cases the centrifugal action causes theparticles to drift to the outer circumference of the flow area adjacentto the inner wall of the separator housing, which is called theseparation area. The time period for the particles to drift to thisouter circumference of the flow area determines the length of thetubular throat portion 4.

Downstream of the tubular throat portion 4 the condensables enriched‘wet’ fluid components tend to concentrate adjacent to the inner surfaceof the diverging fluid separation chamber 5 and the ‘dry’ gaseous fluidcomponents are concentrated at or near the central axis I, whereupon thewet condensables enriched ‘wet’ fluid components discharged into anouter secondary fluid outlet 6 via a series of slots, (micro)porousportions whereas the ‘dry’ gaseous components are discharged into thecentral primary fluid outlet conduit 7.

In the diverging primary fluid outlet conduit 7 the fluid stream isfurther decelerated so that the remaining kinetic energy is transformedinto potential energy. The diverging primary outlet conduit is equippedwith an assembly of flow straightening vanes 9 to recover thecirculation energy.

While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be readily apparent to, and can be easily made by oneskilled in the art without departing from the spirit of the invention.Accordingly, it is not intended that the scope of the following claimsbe limited to the examples and descriptions set forth herein but ratherthat the claims be construed as encompassing all features which would betreated as equivalents thereof by those skilled in the art to which thisinvention pertains.

1. A cyclonic fluid separator comprising: a tubular throat portion whichis arranged between a converging fluid inlet section and a divergingfluid outlet section that comprises an outer secondary outlet forcondensables enriched fluid components and an inner primary outlet forcondensables depleted fluid components; and a number of swirl impartingvanes for creating a swirling motion of the fluid within at least partof the separator, which vanes protrude from a central body having aninner surface and an outer surface; wherein the central body extendsthrough at least part of the converging fluid inlet section of theseparator, wherein the central body has, at a location upstream of thethroat portion, a larger outer width than the smallest inner width ofthe throat portion.
 2. The separator of claim 1, wherein the tubularthroat portion and the outer surface of the central body aresubstantially coaxial to a central axis of the separator and the swirlimparting vanes protrude from the outer surface of the central body ator near the location upstream of the throat portion.
 3. The separator ofclaim 2, wherein the central body has a substantial circular shape in across-axial direction and comprises upstream of the swirl impartingvanes a nose section of which the diameter gradually increases such thatthe degree of diameter increase gradually decreases in downstreamdirection, and the central body further comprises downstream of theswirl imparting vanes a tail section of which the diameter graduallydecreases in downstream direction along at least part of the length ofthe tail section.
 4. The separator of claim 3, wherein the degree ofdiameter decrease of the tail section of the central body varies indownstream direction such that the tail section has an intermediatesection of which the degree of diameter decrease is smaller than thediameter decrease of adjacent parts of the tail section that are locatedupstream and downstream of the intermediate section.
 5. The separator ofclaim 4, wherein the separator comprises a housing in which the centralbody is arranged such that an annulus is present between the innersurface of the housing and the outer surface of the central body.
 6. Theseparator of claim 5, wherein the width of the annulus varies such thatat the prevailing pressure difference between the inlet section and theoutlet section during normal operation of the separator the fluidflowing through the annulus reaches a supersonic velocity at or near theintermediate section of the tail section of the central body.
 7. Theseparator of claim 3, wherein the tail section comprises an elongatedsubstantially cylindrical downstream end which extends substantiallyco-axial to the central axis through the throat portion and at leastpart of the diverging fluid outlet section of the separator.
 8. Theseparator of claim 7, wherein a number of flow straightening vanes aremounted on the substantially cylindrical downstream end of the tailsection of the central body at a location within the diverging outletsection of the separator downstream of the secondary outlet for liquidenriched fluid components.
 9. The separator of claim 3, wherein theseparator comprises a housing in which the central body is arranged suchthat an annulus is present between the inner surface of the housing andthe outer surface of the central body.
 10. The separator of claim 2,wherein the separator comprises a housing in which the central body isarranged such that an annulus is present between the inner surface ofthe housing and the outer surface of the central body.
 11. The separatorof claim 1, wherein the separator comprises a housing in which thecentral body is arranged such that an annulus is present between theinner surface of the housing and the outer surface of the central body.